Processed drawn implement



AugJ-i, 1957 J. J. RussELL 'ErAL n PROCESSED DRAWN IMPLEMENT Filed Jan.3. 1951 2 Sheets-Sheet 1 exam sunzmce 5 v COATING OXIDE sum-Act! 5 ICOAT MG oxwe sunnce 6 COAT! u a oxloe sum-Ac: 6

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Aug. 6, 1957 Filed Jan. 3. 1951 Z i m Q P m M mm s N F EwA o N P S aw eML H O c AR C B N.- Wm M Ts l F T H H 0N6 6 HA1 a p a A H H @T m w w w wUnited States Patent G PROCESSED DRAWN IMPLEMENT John J. Russell, DesPlaines, and William A. Beck, Itasca, Ill., assignors to National GlacoChemical Corporation, Chicago, 111., a corporation of IllinoisApplication January 3, 1951, Serial N 0. 204,152 4 Claims. (31. 113-420This invention relates to a composite tin coated metallic structure,which may be fabricated into shaped metallic articles provided withprocessed outer surfaces in order to facilitate deep drawing of thearticle and to exhibit a relatively high absorption to convective andradiant energy.

An object of this invention is the provision of a practical process forchemically treating tin and tin base alloys in order to provide theouter surfaces with a compound of tin coating to substantially reducethe amount of friction produced between the tin plated structure and thedrawing tools during the deep drawing operations.

Another object of this invention is to provide a compound of tinintermediate to the tin layer of a tin plated structure, wherein saidcompound of tin iscapable of supporting a lubricating film during thedrawing operation.

A more specific object of this invention is to provide a tin platedstructure with an oxide of tin intermediate to the tin layer of said tinplated structure wherein said oxideof tin, capable of being deformed,remains as an. extended continuous coating throughout the drawingoperation.

Another specific object of this invention is to provide a process forforming a deep drawn baking pan having a continuous oxide of tin coatingcovering the outer surfaces of said baking pan, wherein said oxide oftin enhances the drawability of the tin plated steel structure, and inaddition, provides the baking pan with exterior surfaces capable ofabsorbing radiant energy.

Other objects and advantages of this invention will become apparent asthis description proceeds, particularly when considered in connectionwith the accompanying drawings in which:

Figure 1 is a. face view of a processed tin plated blank for making adrawn baking pan;

Figure 2 is a perspective view of a partially fabricated processed tinplated baking pan, which has been subjected to the first 'step in thedrawing operation;

Figure 3 is a perspective view of a partially fabricated baking pan,which has been subjected to a subsequent drawing operation;

Figure 4 is a perspective view of a finished baking pan made from ablank as thatshown in Figure 1, and with the outer edges trimmed andformed;

Figure 5 is a graphic diagram showing the relative ratio of the combinedoxide coating, tin and tin-iron alloy layerthicknesses versus thecorresponding height of a drawn tin plated bread pan;

Figure 6is a graphic diagram showing the relative ratio of the oxide oftin coating versus the correspondingheight of a drawn tin plated breadpan;

Figure 7 is a photomicrograph cross-sectional view of a portion of atin,plate area, not subjected to deformation, of the bottom of a drawn bakepan showing the relative thicknesses of oxide coating, tin layer andalloy layer (2500Xmagnification) and c Figure 8' is a photomicrographcross-sectional view showing the relative thicknesses of the oxidecoating tin layer and alloy layer of a corresponding tin plate areawherein said area has been subjected to deformation.

Referring now more particularly to the drawings, Figure 1 illustrates atin plated baking pan blank 2 wherein prior to the blanking operationsaid tin plated structure was subjected to a chemical process. In thisprocess a continuous oxide of tin is formed on the exterior surfaces ofthe tin plated structure. This tin plated structure comprises a steelcore having a tin-iron alloy layer intermediate to a tin layer, whichmay be deposited either by the conventional hot dip process or theelectrolytic plating process. The steps illustrated in the chemicalprocess for converting a portion of the tin layer to an oxide of tincoating are described in our copending applications Serial No. 156,671,filed April 18, 1950, now Patent No. 2,738,897 and Serial No. 156,672,filed April 18, 1950, now Patent No. 2,724,526.

The configuration and dimensions of the blank 2 are designed so as toafford sufficient metal during the drawing operation. This blank 2 isblanked in the conventional manner using standard press, tool and dieoperations. The irregular shaped corner contours 4 are designed so as togive sufficient metal to the body of the formed metal article during thesuccessive drawing operations. The outer surfaces of the blank 2 havebeen chemically treated having an oxide of tin coating, generallydesignated by numeral 6, formed thereon.

The blank 2 is treated with a drawing lubricant prior to insertion intothe first operation drawing die set, which has been specificallydesigned for drawing a bake pan. Although the specific design andconstruction of the die set does not constitute any part of thisinvention, the specific skills required in the fabrication of drawnlightgauged metal articles shall be considered unique in the fabricationof drawn processed tin plated articles. The drawing lubricant which hasbeen applied to the blank 2 may consist of numerous compositions such asmetallic soaps, oils, greases, water soluble compounds, and combinationsthereof. We have found numerous compositions of drawing lubricants thatmay be used in the drawing operations. Although we have found that thewater soluble compounds and the metallic soaps are superior, the stepsin the fabrication of a drawn bake pan shall not be limited to the typeor composition of the drawing lubricant.

Figure 2 illustratesthe result produced in the first step in the drawingoperation of a processed drawn bake pan 10. The upper flange 12 has beendeformed to produce a rectangular cavity 14 having side walls 16 and abotminds. The depth of draw, which may be defined as the height of theside wall 16, will be approximately 60% of the final height of the sidewall obtained in the final drawing operation, as shown in Figure 3.

Figure 3 illustrates the configuration of a processed drawn bake pan 10,which has been subjected to the final drawing operation wherein theheight of the side wall 16 has been elongated by the drawing operationto approximately an additional 40% of the final depth. Hold-down grooves20 have been formed on the outer flanges 12, in order to facilitate theflow of metal from the contour edges 4 of the drawing blank 2, so as toacquire sufficient metal. We have found that the hold-down grooves 20tend to restrain the flow of metal along the side walls 16 and directthe flow of metal along the corners 22.

Figure 4 illustrates the final fabricated shape of a processed drawnbake pan 10 wherein the outer flanges 12 have been trimmed, formed andcurled, so that the bake pan 10 may be inserted into a conventionalmultiple baking pan set.

Drawing, forming and similaroperations require pressures sufiicient toexceed the elastic limit of the base metal stock and effect permanentchanges in its contour and size. The pressures so exerted must notexceed the ultimate strength or the breaking point of the material orthe result will be scrap. For instance, in these operations theplasticity of the metal permits it to flow into shapes quite differentfrom those existing originally. However, the pressures on the punch andthe die must be definitely controlled while blank holding pressures mustbe lessened at times or even completely released. In addition, dieconsiderations relative to drawing, such as die clearances, must becarefully determined for drawing, forming and related operations,because the clearance vitally affects the success of the draw. Forexample, insufficient clearance or improper radii may .cause tearing ofthe stock, cracking of the work at corners, damage to the dies and otherdifliculties; while excessive clearances may lead to too much metal inthe corners, cracking or bursting of the die, incomplete filling of thedie, and generally poor draws. Improper clearances also have an effecton the tonnage requirements of the press operation. A change in thephysical characteristics of the stock is likely to have a marked effecton the behalf of the dies. Difiiculties due to clearances in certaininstances may be somewhat alleviated in the press room by variouslubrication expedients.

We have found that in the fabrication of tin plated articles it has beenextremely difiicult to obtain a continuous coating of the tin layer overthe entire drawn surfaces of the drawn bake pan 10. In addition, we havefound that our percentage of rejects, such as breakage, tears and thelike, has been extremely high, in the neighborhood of 18 to 23%. We havetaken into consideration the various drawing parameters in these drawingoperations and successful production runs have not been obtained. Inaddition, many types of lubricants and drawing compounds have been usedwithout beneficial results.

The reason for such varying results may be attributed to the nature oftin plate. The tin layer is extremely soft and plastic as compared tothe intermediate tin-iron alloy layer and the steel basis. By subjectingthe tin plate to deformation, the continuous tin layer, being extremelyfluid under drawing pressures, tends to break down and separate leavingthe alloy layer and steel basis exposed. Since the alloy layer and steelbasis are subject to a high corrosion rate, it is highly desirable toretain a continuous layer of tin over the outer surfaces of the drawnarticle in order to substantially reduce corrosion.

By the introduction of a compound of tin coating contiguous to the tinlayer, we have been able to obtain excellent results in the fabricationof deep drawn tin plated articles. We have found that the percentage ofrejects has been substantially reduced to approximately 3 to 5%; therehas been a substantial reduction in the consumption of power in the deepdrawing operation due to the decreasing amount of friction between thearticle and the die; the speed of the drawing operation has beenenhanced; and there has been a substantial increase in the life of thetools and dies due to a reduction of galling action on the dies.

The compound of tin coating 6 may be generally defined as the metastableform of the oxide of tin, although we have found other tin compounds,such as the phosphates and sulfates, are adaptable in this operation.

We have found that the oxide of tin exhibits superior drawing propertiesrelative to the tin plated article than do other compounds of tincoatings; and in addition, the oxide of tin coating performs anadditional function insomuch that it exhibits a high degree of heatabsorption when subjected to radiant energy.

The chemical process utilized in converting a portion of the tin or thetin alloy surfaces to a compound of tin coating, preferably themetastable form of an oxide of tin, is set forth in the aforesaidcopending applications. This process consists of an-odically convertingthe tin or tin alloy surfaces electrolytically to a metastable form ofthe oxide of tin. Numerous process solution parameters, such ascomposition, concentration, temperature and time of immersion are setforth; and the chemical process shall not be limited to any specificcomposite group of parameters.

The metastable oxide of tin composition exhibits interference colorswhen the coating is less than about seven microns thick. We have foundthat satisfactory results are obtained when we use a coating thicknessgreater than seven microns and less than about 40 microinches. Figure 7illustrates a photomicrograph showing an opaque oxide coating 6a whichhas a thickness of approximately 18 microinches thick. The oxide coatingwas formed on one and one-half pound tin plate, using the previouslydisclosed chemical treatments. It shall be noted that the oxide coating6a is substantially greater in thickness than the tin-iron alloy layer28. Intermediate to the tin-iron alloy layer 28 and the opaque oxidecoating 6a is the tin layer 30. The steel base metal is identified bynumeral 32; and the copper mounting 34 is used to, back' up the tinplate so that a well defined boundary may be secured while preparingthese photomicrographic samples.

One and one-half pound tin plate generally is defined as having a tinand tin alloy layer of combined thickness of approximately 90microinches. Since a portion of the tin layer 30 has been converted tothe metastable form of the oxide of tin 6a, Figure 7 illustrates therelative proportions of these various compositions and their relativethicknesses. The photomicrograph illustrated in Figure 7 is a sectionalarea taken from the bottom of the drawn pan 10, wherein this area hasnot been subjected to deformation.

As can be noted from the illustration, the tin layer 30 constitutes asubstantial thickness of the combined tintin alloy layer and coating.The thickness of the tin layer 30 approximates from about 60 tomicroinches.

Figure 8 illustrates an oxide coated one and one-half pound tin platearea, which has been subjected to deformation. This photomicrograph wastaken from a sectionalradius area 36 as shown in Figure 4. The compositetin plate structure in Figure 8 comprises a copper mounting plate 38,the oxide coating 6b, tin layer 42, tin iron alloy layer 44, and thesteel base 46. It shall be noted that the combined thickness of theoxide coating 6b, tin layer 42 and the alloy layer 44 have beensubstantially reduced from a thickness of about microinches to about 65microinches. There has been approximately a reduction of one-third ofthe total thickness of the combined composition. It further shall benoted that the tin layer 30 has been substantially reduced in thickness.Since these photographs were taken at a magnification of approximately2500X, the relative thicknesses of the oxide coatings 6a and 6b and thetin iron alloy layers 28 and 44 do not illustrate a substantial,reduction in thickness. Although there has been a substantial reductionof approximately 50% in the thickness of the oxide coating 6a, thevariation may be interpreted to poor definition and focus in thephotomicrograph.

Figure 5 is a graph illustrating the variation in the combinedthicknesses of the oxide coating, tin layer and iron alloy layer, takenalong the side wall 16 of the drawn bake pan 10 from the upper bead 17,around the radius 36, to the bottom 18 of the pan 10. These combinedthicknesses were ascertained by two methods, namely, chemical analysisand relative non-magnetic thickness.

With reference to the graph as shown in Figure 5,,the abscissa definesthe relative height of the side 16 of the bread pan 10 and the ordinatedefines the combined thicknesses of the oxide coating, tin layer andtin-iron alloy layer. In following the curve along the bottom 18, thecombined thickness is approximately 90 microinches and graduallydecreases along the bottom radius 36 t0 approximately 65 microinches,gradually increases and obtains the maximum thickness of approximately90 microinches and decreases along the bead 17 to approximately 65microinches, and then increases to the maximum thickness along theflanges 12. In interpreting this diagram, it shall be noted that thebottom 18, the sides 16 and the flanges 12 have been subjected tosubstantially no deformation. The combined thicknesses along the bottomradius 36 and the head 17 have been reduced to approximately two-thirdsof the original thickness. It shall be noted that the photornicrographillustrated in Figure 8 still retains over the bottom radius 36 asubstantial amount of the tin layer 42, and other photomicrographs, notillustrated, indicate that similar results were obtainable along thebead 17.

Figure 6 illustrates the curve of the relative thickness of the tinoxide layer 6 versus the relative height of the bread pan 10. It shallbe noted from the diagram that the maximum thickness of the oxide layer6 of about 15 microinches along the bottom 18, side 16 and flange 12 hasbeen reduced in thickness, due to deformation, to about 8 microinchesalong the bottom radius 36 and the bead 17. It shall be noted incomparing the photomicrographs that there is a greater percentagereduction in the oxide coatings 6a and 6b as compared to the tin layers30 and 42, and this may be based upon the relative degrees of plasticityof the higher melting oxide of tin composition as compared to the lowermelting point of tin.

In interpreting these relative results, we have found that the presenceof the oxide coatings 6a and 61) have greatly enhanced the drawabilityof tin plate because the oxide coatings 6a and 6b, due to a highermelting point and toughness, afford an intermediate stratum between thelow melting tin layers and the punch and die used in the drawingoperation. Since tin has a melting point of approximately 449 F. We havefound that there has been a considerable amount of galling of the diesbecause tin of itself has an extremely high tendency to wet metalsurfaces when no oxide interface is present. In addition, due to therelatively high temperatures created in the drawing operations, tinwithout the presence of the oxide interface tends to disperse unevenlyover the entire drawing area so that in areas of greater deformation wehave found that practically no tin remains on these surfaces. It is wellknown in the art that tin affords substantial corrosion resistance andit is highly desirable to retain the tin uniformly over the entiresurface of the drawn article, such as a cooking utensil or bakingimplement. The tin-iron alloy, as well as the steel base, are subject torapid corrosion rates.

In addition, the oxide of tin coating 6 performs another function. Wehave found that by preferably using the metastable form of the oxide oftin coating 6 during the drawing operation, and then subjecting thedrawn bake pan 10 to an elevated temperature, less than the meltingpoint of tin, the black metastable form of oxide of tin can be convertedto an opaque olive-green stable form of oxide of tin. In addition, thereare numerous scratches and draw marks produced over the entire surfacearea during the drawing operation. However, during the conversion cyclefrom the metastable to the stable form of the oxide of tin, theseimperfections are cured so that the final product exhibits a continuousoxide coating of tin 6 over the entire surface. We have found thatsatisfactory results have been obtained by first converting themetastable oxide of tin to the stable form, and then producing the drawnarticle or implement. These forms of oxide of tin coatings 6 exhibitsuperior absorptive properties when the article is subjected toconvective and radiant heat, such as required in the baking of bread.

While for the purposes of illustrating and describing the presentinvention certain preferred embodiments have been shown in the drawing,it is to be understood that the invention is not to be limited therebysince such variations are contemplated as may be commensurate 7 with thespirit and scope of the invention set forth in the accompanying claims.

We claim as our invention:

1. A method of fabricating a tinned blank consisting of a base metalhaving a tin or tin alloy layer deposited thereon into a processed drawntinned article comprising the steps of chemically treating the tin layerso as to partially convert a portion of the tin layer into an oxide oftin coating, coating a portion of said oxide of tin coating with adrawing lubricant and then subjecting the treated tinned blank to adrawing operation whereby the metallic tin layer is substantially intactbetween said base metal and said oxide of tin coating.

2. A method of producing a processed drawn baking implement comprisingthe steps of chemically treating a tin plated steel base blank whereby aportion of the tin layer is partially converted to the meta-stable formof the oxide of tin, coating a portion of said oxide of tin coating witha drawing lubricant, deforming said treated blank into a shapedimplement whereby the remaining metallic tin layer is substantiallyintact between said steel base and said oxide of tin layer, trimmingsaid deformed shaped implement and then forming the flanges of saiddeformed shaped implement into a baking implement.

3. A method of producing a processed drawn baking implement comprisingthe steps of chemically treating a tin plated steel base blank whereby aportion of the tin layer is partially converted to the meta-stable formof the oxide of tin, coating a portion of said oxide of tin coating witha drawing lubricant, deforming said treated blank into a shapedimplement whereby said remaining metallic tin layer is substantiallyintact between said steel base and said oxide of tin layer, trimmingsaid deformed shaped implement, forming the flanges of said deformedshaped implement into a baking implement, and then subjecting saidbaking implement to elevated temperature whereby the metastable oxide oftin is converted to the stable form of the oxide of tin.

4. A method of fabricating a sanitary deep drawn inetallic baking panstructure free of interior folds and crevices, having heat absorptivetin oxide outer coatings comprising the following steps: chemicallytreating a tin coated steel core blank so as to form a tin oxide coatingcoetxensive with the remaining corrosion resistant tin layer, coating aportion of said tin oxide coating with a drawing lubricant, subjectingthe oxide coated steel core blank having corrosion resistant metallictin interposed between said oxide coating and said steel supporting coreto a deep drawing operation, whereby the metallic tin is substantiallyintact between said steel core and said oxide coating.

References Cited in the file of this patent UNITED STATES PATENTS436,883 Wagandt Sept. 23, 1890 499,359 Hall June 13, 1893 2,024,951Schutte Dec. 17, 1935 2,152,516 White Mar. 28, 1939 2,215,165 SumnerSept. 17, 1940 2,245,561 Nelson et al. June 17, 1941 2,346,714 WobbeApr. 18, 1944 2,391,660 Ward Dec. 25, i945 2,462,728 Debs Feb. 22, 19492,471,500 Stewart et al May 31, 1949 FOREIGN PATENTS 300,641 GreatBritain Apr. 7, 1930 OTHER REFERENCES Tinplate, by W. E. Hoare and E. S.Hedges, published in 1945 by Edward Arnold and Company, London, page243.

Metallurgy of Deep Drawing and Pressing, by J. Dudley Jevons, SecondEdition, published 1942 by John Wiley and Sons, Inc., New York, page117.

1. A METHOD OF FABRICATING A TINNED CONSISTING OF A BASE METAL HAVING ATIN OR ALLOY LAYER DESPOSITED THEREON INTO A PROCESSED DRAWN TINNEDARTICLE COMPRISING THE STEPS OF CHEMICALLY TREADING THE TIN LAYER SO ASTO PARTIALLY CONVERT A PORTION OF THE TIN LAYER INTO AN OXIDE OF TINCOATING, COATING A PORTION OF SAID OXIDE OF TIN COATING WITH A DRAWINGLUBRICANT AND THEN SUBJECTING THE TREATED TINNED BLANK TO A DRAWINGOPERATION WHEREBY THE METALLIC TIN LAYER IS SUBSTANTIALLY INTACT BETWEENSAID BASE METTAL AND SAID OXIDE OF TIN COATING.